1. Field of the Invention
The present invention relates generally to a photointerrupter and a method of manufacturing such a photointerrupter and, more particularly, to improvements on the structure of a double mold type photointerrupter and on a method of manufacturing such a photointerrupter.
2. Description of the Background Art
Photointerrupters are of two types, a transmission type and a reflection type. The transmission type photointerrupter is structured such that a light emitting element (mostly an infrared emitting diode) and a light receiving element (a phototransistor or photodiode, or alternatively, an element including such a phototransistor or photodiode integrated with a signal amplifier, a waveform shaping circuit or the like) are disposed to be opposite to each other for detecting a light shielding object which passes between the light emitting element and the light receiving element. The reflection type photointerrupter is structured such that the light emitting element and the light receiving element are aligned for detecting the light shielding object by light reflected from the object. Thus, the photointerrupters are employed to detect the existence of the light shielding object without being in contact with the light shielding object. Recently, photointerrupters are widely applicable to audio apparatus, OA apparatus and the like.
FIG. 1 is a plan view showing a conventional transmission type photointerrupter. FIG. 2 is a cross-sectional view taken along the line II--II of FIG. 1. FIG. 3 is a cross-sectional view taken along the line III--III of FIG. 1. Description will now be made on the structure of the conventional photointerrupter with reference to FIGS. 1, 2 and 3. A light emitting element 1 is mounted on one lead frame 3 provided on the light emission side. A bonding wire 5 is provided to connect between light emitting element 1 and the other lead frame 3 provided on the light emission side. A light receiving element 2 is mounted on one lead frame 4 provided on the light reception side. A bonding wire 5 is provided to connect between light receiving element 2 and the other lead frame 4 provided on the light reception side. Primary moldings 6 and 7 are formed of a light transmissive resin to cover light emitting element 1 and lead frames 3, and light receiving element 2 and lead frames 4, respectively. Primary moldings 6 and 7 are shown in FIGS. 4-6. FIG. 4 is a front view of such primary molding. FIG. 5 is a plan view of the primary molding. FIG. 6 is a cross-sectional view taken along the line VI--VI of FIG. 5. Primary moldings 6 and 7 have convexities or protrusions 6a and 7a, respectively. Convexities 6a and 7a are formed to define a portion through which light passes.
Primary molding 6 on the light emission side and primary molding 7 on the light reception side are unified together by a secondary molding 8 formed of a light shielding resin. This causes optical coupling between light emitting element 1 and light receiving element 2, i.e., convexities 6a and 7a are opposed to each other. Primary moldings 6 and 7 are disposed in secondary molding 8 to expose the surface of convexities 6a and 7a. Thus, a passage 9 of an object to be detected is formed.
As denoted by chain-dotted lines in FIG. 2, lead frames 3 and 4 drawn out from a bottom surface of secondary molding 8 are bent toward respective back surfaces of primary moldings 6 and 7. In such a manner, lead frames 3 and 4 are processed to be attached on a predetermined substrate.
Light emitted from light emitting element 1 passes through convexity 6a and then reaches opposite convexity 7a. The light arrived at convexity 7a is detected by light receiving element 2. If any light shielding object is provided along passage 9 formed between convexities 6a and 7a, then the light emitted from light emitting element 1 is intercepted and thus not detected by light receiving element 2. Thus, the transmission type photointerrupter has a sensing function utilizing light.
FIG. 7 is a side view of a conventional transmission type photointerrupter attached on the substrate. FIG. 8 is a plan view of the conventional transmission type photointerrupter attached on the substrate. Lead frames 3 on the light emission side and lead frames 4 on the light reception side, extending outward from a primary molding 8, are attached on a substrate 100. A predetermined conductor pattern 101 is formed on substrate 100. Each of lead frames 3 and 4 is positioned within the range of conductor pattern 101. Each of lead frames 3 and 4 adheres to conductor pattern 101 by a reflow solder.
In the conventional photointerrupter, a gap is produced between each of lead frames 3 and 4 and a lower surface of secondary molding 8. When the photointerrupter is automatically mounted on substrate 100, an external force such as pressing or the like for the automatic mounting is applied to the photointerrupter. The application of the external force sometimes causes deformation of lead frames 3 and 4. FIGS. 9 and 10 are side views showing a photointerrupter with deformed lead frames. When only one lead frame 3 is deformed as shown in FIG. 9, uniform soldering cannot be made for adhesion between lead frames 3 and 4 and conductor pattern 101. In addition, the photointerrupter is connected with an inclination to substrate 100. When lead frames 3 and 4 are deformed as shown in FIG. 10, the height of the photointerrputer is compressed. This results in a degradation in detection characteristics, i.e., sensing function of the photointerrupter.
Moreover, since the gap is made between lead frames 3 and 4 and the lower surface of secondary molding 8, the following problem occurs in attachment of the photointerrupter to the substrate. Referring to FIG. 8, the size of conductor pattern 101 formed on substrate 100 is larger than that of each of lead frames 3 and 4. Each lead frame 3, 4 adheres to conductor pattern 101 by a reflow solder. In that case, with the reflow solder melting, the photointerrupter, i.e., secondary molding 8 is sometimes displaced in a direction of rotation shown by the arrow of FIG. 8 due to surface tension or the like of the solder.
FIGS. 11A--11C are cross-sectional views of a metal mold illustrated in accordance with a lead frame bending process in the conventional photointerrupter. With reference to FIG. 11A, each of lead frames 3 and 4 extends from the lower surface of secondary molding 8. Punches 22a and 22b are inserted between lead frames 3 and 4 as shown by the arrow. A metal mold 21 is in close contact with an outer side surface of secondary molding 8 and a proximal end of each lead frame 3, 4.
Referring to FIG. 11B, a spacing between lead frames 3 and 4 is expanded by punches 22a and 22b. Then, punches 22a and 22b move in opposite directions as shown by the arrows.
Thus, lead frames 3 and 4 are bent as shown in FIG. 11C.
In the above-described lead frame bending process, it is necessary to reduce a thickness D of a convex portion of metal mold 21 for receiving punches 22a and 22b in order to reduce a dimension W of the proximal end of each lead frame 3, 4 as shown in FIG. 11A. However, there is a limitation in reducing thickness D with respect to the strength of the forming metal mold.
In addition, if a spacing L between lead frames 3 and 4 decreases in the above lead frame bending process, a thickness T of each of punches 22a and 22b must be reduced. However, there is a limitation in reducing thickness T with respect to the strength of the punches.